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22 .TH PCAP_GET_SELECTABLE_FD 3PCAP "5 April 2008"
24 pcap_get_selectable_fd \- get a file descriptor on which a select() can
25 be done for a live capture
29 #include <pcap/pcap.h>
33 int pcap_get_selectable_fd(pcap_t *p);
37 .B pcap_get_selectable_fd()
38 returns, on UNIX, a file descriptor number for a file descriptor on
44 to wait for it to be possible to read packets without blocking, if such
45 a descriptor exists, or \-1, if no such descriptor exists. Some network
51 .BR pcap_open_live() ,
56 (for example, regular network devices on FreeBSD 4.3 and 4.4, and Endace
57 DAG devices), so \-1 is returned for those devices.
61 FreeBSD prior to FreeBSD 4.6;
63 NetBSD prior to NetBSD 3.0;
65 OpenBSD prior to OpenBSD 2.4;
67 Mac OS X prior to Mac OS X 10.7;
72 do not work correctly on BPF devices;
73 .B pcap_get_selectable_fd()
74 will return a file descriptor on most of those versions (the exceptions
75 being FreeBSD 4.3 and 4.4), but a simple
79 will not indicate that the descriptor is readable until a full buffer's
80 worth of packets is received, even if the read timeout expires before
81 then. To work around this, an application that uses
85 to wait for packets to arrive must put the
87 in non-blocking mode, and must arrange that the
91 have a timeout less than or equal to the read timeout,
92 and must try to read packets after that timeout expires, regardless of
97 indicated that the file descriptor for the
99 is ready to be read or not. (That workaround will not work in FreeBSD
100 4.3 and later; however, in FreeBSD 4.6 and later,
104 work correctly on BPF devices, so the workaround isn't necessary,
105 although it does no harm.)
109 doesn't work on character special files, including BPF devices, in Mac
110 OS X 10.4 and 10.5, so, while
112 can be used on the descriptor returned by
113 .BR pcap_get_selectable_fd() ,
115 cannot be used on it those versions of Mac OS X. Kqueues also don't
116 work on that descriptor.
118 but not kqueues, work on that descriptor in Mac OS X releases prior to
121 and kqueues work on that descriptor in Mac OS X 10.6 and later.
123 .B pcap_get_selectable_fd()
124 is not available on Windows.
126 A selectable file descriptor is returned if one exists; otherwise, \-1
129 pcap(3PCAP), select(2), poll(2)